1. Field of the Invention
The present invention relates to a reliability testing method of a dielectric thin film. More particularly, the present invention relates to a method for testing the reliability of a dielectric thin film layer by using an exponential current ramp test (ECR).
2. Description of the Related Art
Reliability of thin dielectric films such as silicon dioxide has been a major concern throughout the history of MOS integrated circuit production. The quality of a gate oxide layer is of great importance, which is particularly true when more stringent customer requirements are demanded. It is essential to monitor oxide performance in production to provide early warning of reliability excursions and provide measures toward continuous process improvement.
It is widely accepted that highly accelerated measurement of gate oxide charge-to-breakdown (Q.sub.BD) is employed as a process monitor/control parameter. Traditionally, Q.sub.BD is determined by using a constant current stress test (CCS). In a CCS test, a stress current density is held constant, and time-to-breakdown (t.sub.BD) is measured and multiplied by a current density to obtain a Q.sub.BD. Although the determination of Q.sub.BD through CCS is simple and straightforward, the measurement is time consuming. Thus, the application of quick monitoring and improvement of gate oxide layer quality and integrity is limited.
On the other hand, an exponential current ramp test (ECR) provides a fast way to determine the Q.sub.BD. In an ECR test, a current is injected into the oxide in exponential steps until a breakdown occurs.
The ECR test provides a way of monitoring Q.sub.BD in a very short measurement time with reasonable resolution of early failures. Thus, for production monitors, the ECR test has a significant speed advantage over the CCS test. Accordingly, the ECR test should replace the traditional CCS test in industry for fast wafer level reliability (fWLR) of Q.sub.BD evaluation as long as it can well correlate with the CCS test.